Initial commit. Still WIP

Author: luisquintanilla

docs/core/whats-new/dotnet-9/overview.md

@@ -53,7 +53,37 @@ The .NET 9 SDK introduces _workload sets_, where all of your workloads stay at a
 
 For more information, see [What's new in the SDK for .NET 9](sdk.md).
 
-## AI and Machine Learning
+## AI Building Blocks and Fundamentals
+
+### Tokenizers
+
+The Microsoft.ML.Tokenizers library provides .NET developer with capabilities for encoding and decoding text to tokens. For AI scenarios, this is important to manage context, calculate cost, and pre-process text when working with local models.
+
+The latest release introduces significant new capabilities:
+
+- Tokenizers
+  - SentencePiece
+  - WordPiece
+  - BERT
+  - CodeGen
+- Built-in tokenizers for the following models:
+  - GPT (3, 3.5, 4, 4o, o1)
+  - Llama
+  - Phi
+
+### Tensors
+
+<!-- TODO -->
+
+### Microsoft.Extensions.AI
+
+<!-- TODO -->
+
+### Microsoft.Extensions.VectorData
+
+<!-- TODO -->
+
+## ML.NET
 
 ML.NET is an open-source, cross-platform framework that enables integration of custom machine-learning models into .NET applications. The latest version, ML.NET 4.0, adds [additional tokenizer support](../../../machine-learning/whats-new/overview.md#additional-tokenizer-support) for tokenizers such as Tiktoken and models such as Llama and CodeGen. <!--Add info about `Tensor<T>` here and in what's new for ML.NET.-->